Various biosynthetic products, for example, fine chemicals, such as, inter alia, amino acids, vitamins, carotenoids, but also proteins, are produced by natural metabolic processes in cells and used in various branches of industry, including the human and animal food, cosmetics, and pharmaceutical industries.
Production thereof on a large scale takes place in part by means of biotechnological processes using microorganisms which have been developed in order to produce and secrete large amounts of the particular desired substance.
For example, carotenoids are synthesized de novo in bacteria, algae and fungi. In recent years there have been increasing attempts to utilize oleaginous yeast and fungi as organisms for producing fine chemicals, especially for producing vitamins and carotenoids.
Carotenoids, such as lutein, zeaxanthin, astaxanthin and beta carotene, are extracted for example from Yarrowia as so-called oleoresin. These oleoresins are used both as constituents of dietary supplements and in the feed sector.
Ketocarotenoids, meaning carotenoids which comprise at least one keto group, such as, for example, astaxanthin, canthaxanthin, echinenone, 3-hydroxyechinenone, 3′-hydroxyechinenone, adonirubin and adonixanthin, are natural antioxidants and pigments which are produced by some algae, organisms and microorganisms as secondary metabolites.
Biosynthesis of these molecules in organisms which is able to produce them, such as yeast and bacteria, has been characterized in details (Weinheim et al., (1996) Ullmann's Encyclopedia of Industrial Chemistry, “Vitamins”, Vol. A27, pp. 443-613; Biochemical Pathways: An Atlas of Biochemistry and Molecular Biology, John Wiley & Sons, Michal, G. Ed. (1999); Ong, A. S., Niki, E. and Packer, L., (1995) “Nutrition, Lipids, Health and Disease” Proceedings of the UNESCO/Confederation of Scientific and Technological Associations in Malaysia and the Society for Rree Radical Research-Asia, held on Sep. 1-3, 1994, in Penang, Malaysia, AOCS Press, Champaign, Ill. X, 374 S). In particular, biosynthesis of carotenoids in Yarrowia is described in WO2006/102342.
Owing to their coloring properties, the ketocarotenoids and especially astaxanthin are used as pigmenting agents in livestock nutrition, especially in the rearing of trout, salmon and shrimps.
An economical biotechnological process for producing natural biosynthetic products and especially carotenoids is therefore of great importance.
WO 2008/042338 discloses a number of promoters used for overexpression of carotenoid biosynthesis genes in Yarrowia. 
One type of promoters is disclosed in EP 0220864 A. This publication describes a Yarrowia lipolytica yeast promoter XPR2. The XPR2 yeast promoter is only active at pH above 6.0 on media lacking preferred carbon and nitrogen sources and full induction requires high levels of peptone in the culture medium (Ogrydziak, D. M., Demain, A. L., and Tannenbaum, S. R., (1977) Biochim. Biophys. Acta. 497: 525-538; Ogrydziak, D. M. and Scharf, S. J., (1982) Gen. Microbiol. 128: 1225-1234.)
Another type of promoters for expressing genes in yeast, as for example Yarrowia, is described in WO 1997/044470.
The promoters used to date cannot, however, fully satisfy the requirement for high expression in Yarrowia. There was consequently a need to provide promoters which better satisfy the requirements.
Therefore, an object of the present invention is to provide new improved yeast promoters, especially for use in expression cloning in yeast, but also for heterologous expression of desired fine chemicals as defined above in an expression system of choice.